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# Bullet Weight vs. Bearing Surface

#1
12-18-2010, 05:19 PM
 Silver Member Join Date: May 2009 Location: Central Oregon Posts: 314
Bullet Weight vs. Bearing Surface

Which is the more critical measurement, weight or bearing surface when segregating bullets?

I have separated bullets by .001" bearing surface, then weighed. I am finding a variance of +/- .2gr. within each group.

This is using the SMK 300gr. bullets.

Thanks,
Ray
__________________
"One of the ordinary modes, by which tyrants accomplish their purposes without resistance, is, by disarming the people, and making it an offense to keep arms."
-- Constitutional scholar and Supreme Court Justice Joseph Story, 1840

Last edited by padd54; 12-18-2010 at 05:56 PM..
#2
12-18-2010, 06:01 PM
 Platinum Member Join Date: Aug 2003 Location: NC, oceanfront Posts: 2,840
Re: Bullet Weight vs. Bearing Surface

You could analyze every possibility here, and gain nothing with it (other than understanding).
A 300smk is both really heavy, and really long. So this variance amounts to microscopic percentages(0.2/300 = 0.07%).
Then there is the possibility that you're not actually isolating bearing, but getting some base angle and/or ogive radius variance affecting your datums of measurement. So then the question is which specifically, by exactly how much, and what are the affects of every combination for real.

I wouldn't worry about it in this case.

Last edited by Mikecr; 12-18-2010 at 06:07 PM..
#3
12-18-2010, 06:21 PM
 Silver Member Join Date: May 2009 Location: Central Oregon Posts: 314
Re: Bullet Weight vs. Bearing Surface

Thanks, but I want to assemble the "perfect" cartridge.

So, with that in mind, which measurement would be the more critical and have the greatest impact on ballistics?
__________________
"One of the ordinary modes, by which tyrants accomplish their purposes without resistance, is, by disarming the people, and making it an offense to keep arms."
-- Constitutional scholar and Supreme Court Justice Joseph Story, 1840
#4
12-18-2010, 07:01 PM
 Platinum Member Join Date: Jan 2004 Location: Blackfoot, Idaho Posts: 7,853
Re: Bullet Weight vs. Bearing Surface

The goal is to achieve an Extreme Spread in very low teens or single digits. The lower the better.

Bearing surface variations is commonly suspected as the culprit. Vertical stringing at long distances is proportional to velocity spread.

However, variations in bc are also a factor. Thus included with bearing surface measurement is meplat trimming. There are those here that say it makes a difference beyond 600 yards. I tend to agree with them.

A bit poorer but uniform bc is certainly better than a varying bc from shot to shot.
__________________
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!
#5
12-18-2010, 08:05 PM
 Silver Member Join Date: May 2009 Location: Central Oregon Posts: 314
Re: Bullet Weight vs. Bearing Surface

Thanks, so I need to trim the meplats(tips) after I determine their Bearing Surface and disregard the weights ?

How much do I take off, and do they all need to be the same OAL?

I don't mind doing the detail work, it will be awhile before the weather is mild enough for me go out shooting.
__________________
"One of the ordinary modes, by which tyrants accomplish their purposes without resistance, is, by disarming the people, and making it an offense to keep arms."
-- Constitutional scholar and Supreme Court Justice Joseph Story, 1840
#6
12-18-2010, 08:12 PM
 Platinum Member Join Date: Aug 2003 Location: NC, oceanfront Posts: 2,840
Re: Bullet Weight vs. Bearing Surface

Well, this side of carefully known extremes, AND competent ballistic lab validation, it's all conjecture and folklore.
It could not even be guessed at without painstaking isolation of each specific variance.
For example, a bullet that is heavier 'might' have a lower MV, but a higher BC, combined with a barrel time that releases a bullet on a higher trajectory. Or it may have a higher MV depending on the grove/bore seal and friction, and bullet's extra weight contribution to it's bearing or diameter or length, and/or resulting case fill/powder. This of course completely changes if your bullet's are coated, and might help if the extra .2gr is producing a smaller meplat..
More bearing might mean anything to YOUR bore/groove. It might like the sealing, or hate the friction. The small tension change from extra bearing seated, could put you in & out of an edgy tune.

Every combination of internal and external ballistic affects here could sum to zero, or an extreme, and it's unpredictable without isolation and local validation.
You're soliciting conjecture.
There, I said it...
#7
12-18-2010, 08:20 PM
 Silver Member Join Date: May 2009 Location: Central Oregon Posts: 314
Re: Bullet Weight vs. Bearing Surface

Thanks, now I completely understand and can sleep easy.

And you are correct in your conclusion, I am soliciting conjecture. That is the purpose of 90% of the posts on any forum I would say.
__________________
"One of the ordinary modes, by which tyrants accomplish their purposes without resistance, is, by disarming the people, and making it an offense to keep arms."
-- Constitutional scholar and Supreme Court Justice Joseph Story, 1840

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